To easily analyze frictional energy by measuring the in-plane pressure and vertical pressure at one point of a tread by the rolling of a tire, determining static frictional force, and determining the frictional energy in a sliding region having a value larger than the primary maximum value of this static frictional force.

The in-plane pressure, vertical pressure, and slip quantity for the ground length L of one point of a tire are measured and calculated, and static frictional force R(L) is determined based on the obtained in-plane pressure and vertical pressure. The primary maximum value Rm of the static frictional force R(L) is determined afterwords. This Rm is a value nearest to a ground front end section A in the primary maximum value. A ground position exceeding the maximum static frictional force Rm is a limit value C, the ground range LR to a ground rear end section B thereafter becomes a sliding region where frictional energy occurs. The sum total of the work is determined by integration in the whole sliding region LR, and frictional energy can be determined by multiplying the sum total by the prescribed proportional constant.